1. Field of the Invention
This invention relates generally to photographic cameras and, more particularly, to passive automatic focus/automatic exposure systems for cameras.
2. Description of the Related Art
Cameras that require no adjustments from users before taking photographs are very. inexpensive and easy to use, and therefore are quite popular with consumers. These cameras often have a fixed lens focus distance, shutter speed, and aperture diameter. For improved picture-taking with no loss in convenience, consumers typically purchase flash-equipped cameras with variable focus, shutter, and aperture mechanisms and automatic exposure and automatic focus systems. Automatic exposure systems detect the amount of ambient light in the photographic scene and adjust one or more exposure parameters such as shutter speed, aperture opening, and flash setting to obtain optimal exposures for the detected light level. Automatic focus systems typically include ranging systems that determine the distance from the camera to a subject and automatically set the focus of the camera objective lens in accordance with the determined distance. Generally, the distance to the subject can be measured by a light- or sound-emitting system, comprising an active system, or the distance can be measured by the ambient light received from the photographic scene, comprising a passive, split-image rangefinder system.
Active ranging systems generally provide good accuracy, but require relatively expensive components, including an emitter that produces a beam of energy directed into a photographic scene, a beam receiver that detects the reflected beam from a subject in the scene, and a control system that provides power to the emitter and processes information from the beam receiver to determine the distance to the subject. These systems add cost and increase the difficulty of packaging the camera components into a compact camera size. Passive split-image rangefinder systems can require complex data manipulation and correlation functions to make the calculations necessary to convert received ambient light levels into object distances. Sophisticated cameras that provide both automatic lens focus and exposure control features are very convenient to use and provide good results, but can be rather complex and expensive. See, for example, U.S. Pat. No. 4,345,825 to Matteson and U.S. Pat. No. 5,017,955 to Kotani.
Cameras that provide the benefits of automatic exposure and automatic focus without the complexity and expense of more sophisticated ranging systems are desirable. For example, U.S. Pat. No. 4,710,013 to Wong assigned to W. Haking Enterprises of Hong Kong describes a camera with a relatively simple passive automatic focus and automatic exposure capability in which the ambient light level is detected as being one of two levels and limited camera adjustments are made accordingly. A detected lower light level places the camera in a flash mode in which a flash unit is activated and lens focus distance is set to a minimum setting with maximum aperture, and a higher light level places the camera in a daylight mode in which the flash unit is turned off and the lens focus distance is set to a maximum setting with minimum aperture.
Although an automatic lens focus and automatic exposure control system such as described in the Haking patent is not excessively complex and expensive and also generally provides satisfactory photographs, it would be desirable to provide greater adjustment capability without the relatively great complexity and expense of the other systems described above. For example, with only two light levels from which to index camera adjustments, somewhat incorrectly exposed exposures can be produced, especially in high contrast situations. Greater exposure parameter adjustment would help provide exposures that are more evenly illuminated.
From the discussion above, it should be apparent that there is a need for a relatively simple and inexpensive automatic lens focus and automatic exposure control system that provides quick, relatively accurate lens focus distance setting and improved exposure under a variety of lighting conditions. The present invention fulfills this need.